If you cast a creature spell of the chosen type, Door of Destinies will get a charge counter before the creature enters the battlefield. The creature will enter the battlefield with the additional boost to its power and toughness.

7/1/2013

Creature types, such as Human or Sliver, appear after the dash on the type line of creatures. Notably, artifact is not a creature type. A creature may have more than one creature type, such as Goblin Warrior. Such a creature would benefit from Door of Destinies if the chosen creature type was Goblin or Warrior.